Purpose

Tumor levels of thymidylate synthase (TS), a target of 5-fluorouracil (5-FU)-based chemotherapy for colorectal cancer, have been studied as a predictive or prognostic biomarker with mixed results.

Patients and methods

Tumor TS levels were prospectively evaluated in two adjuvant therapy trials for patients with resected stage II or III colon cancer. TS expression was determined by standard immunohistochemistry and by automated quantitative analysis. Tumor mismatch repair deficiency (MMR-D) and BRAF c.1799T > A (p.V600E) mutation status were also examined. Relationships between tumor TS, MMR-D, and BRAF mutation status, overall survival (OS), and disease-free survival (DFS) were investigated in the subset of stage III patients.

Results

Patients whose tumors demonstrated high TS expression experienced better treatment outcomes, with DFS hazard ratio (HR) = 0.67, 95% confidence interval (CI) = 0.53, 0.84; and OS HR = 0.68, 95% CI = 0.53, 0.88, for high versus low TS expression, respectively. No significant interaction between TS expression and stage was observed (DFS: interaction HR = 0.94; OS: interaction HR = 0.94). Tumors with high TS expression were more likely to demonstrate MMR-D (22.2% vs. 12.8%; p =  .0003). Patients whose tumors demonstrated both high TS and MMR-D had a 7-year DFS of 77%, compared with 58% for those whose tumors had low TS and were non-MMR-D (log-rank p =  .0006). Tumor TS expression did not predict benefit of a particular therapeutic regimen.

Conclusion

This large prospective analysis showed that high tumor TS levels were associated with improved DFS and OS following adjuvant therapy for colon cancer, although tumor TS expression did not predict benefit of 5-FU-based chemotherapy. The Oncologist 2017;22:107-114Implications for Practice: This study finds that measurement of tumor levels of thymidylate synthase is not helpful in assigning specific adjuvant treatment for colorectal cancer. It also highlights the importance of using prospective analyses within treatment clinical trials as the optimal method of determining biomarker utility.

Purpose

The TP53 tumor suppressor is frequently mutated in colon cancer, but the influence of such mutations on survival remains controversial. We investigated whether mutations in the DNA-binding domain of TP53 are associated with survival in stage III colon cancer.

Experimental design

The impact of TP53 genotype was prospectively evaluated in Cancer and Leukemia Group B 89803, a trial that randomized stage III colon cancer patients to receive adjuvant 5-fluorouracil/leucovorin (5FU/LV) or 5FU/LV with irinotecan (IFL).

Results

TP53 mutations were identified in 274 of 607 cases. The presence of any TP53 mutation did not predict disease-free survival (DFS) or overall survival with either adjuvant regimen when men and women were considered together or as separate groups. However, outcome differences among women became apparent when tumor TP53 genotype was stratified as wild-type versus zinc- or non-zinc-binding mutations in the TP53 DNA-binding domain. DFS at 5 years was 0.59, 0.52, and 0.78 for women with TP53 wild-type tumors, and tumors with zinc- or non-zinc-binding mutations, respectively. Survival at 5 years for these same women was 0.72, 0.59, and 0.90, respectively. No differences in survival by TP53 genotype were observed in men.

Conclusions

The presence of any TP53 mutation within the DNA-binding domain did not predict survival in stage III colon cancer. However, TP53 genotype was predictive of survival in women following adjuvant therapy. Future colon cancer therapeutic trials, with inclusion of correlative molecular markers, should be designed to permit evaluation of survival and/or response to treatment in women separately from men.

The International Cancer Genome Consortium (ICGC) was launched to coordinate large-scale cancer genome studies in tumours from 50 different cancer types and/or subtypes that are of clinical and societal importance across the globe. Systematic studies of more than 25,000 cancer genomes at the genomic, epigenomic and transcriptomic levels will reveal the repertoire of oncogenic mutations, uncover traces of the mutagenic influences, define clinically relevant subtypes for prognosis and therapeutic management, and enable the development of new cancer therapies.